Devices A and B are connected independently to a variable frequency alternating voltage source as shown. The current in A is ahead of the voltage whereas it legs behind the voltage in B. () Identify the devices A and B. (1) How will the current in each of these devices change on decreasing the frequency of the applied voltage? Give reason
Answers
Answer:
A) Phase difference between V and I is
2
π
. So the device can be a capacitor.
B) Curve A represents power P=VI , where the amplitude is equivalent to the multiplication of amplitudes of V and I curve. Curve B is sine curve and represents voltage and curve C is a cosine curve representing the current.
Full cycle of the graph consist of two positive and two negative symmetrical area. So the average power consumed in the circuit is zero.
C) The AC impedance of a capacitor is known as Reactance and as we are dealing with capacitor circuits, more commonly called Capacitive Reactance, X
C
. Graph shows variation of capacitive reactance with frequency.
D) V=V
0
sinωt
Q=CV
Where C is capacitance.
I=
dt
dQ
=C
dt
dV
=CV
0
ωcosωt
Thus there is a
2
π
phase difference between current and voltage.
Explanation:
A) Phase difference between V and I is
2
π
. So the device can be a capacitor.
B) Curve A represents power P=VI , where the amplitude is equivalent to the multiplication of amplitudes of V and I curve. Curve B is sine curve and represents voltage and curve C is a cosine curve representing the current.
Full cycle of the graph consist of two positive and two negative symmetrical area. So the average power consumed in the circuit is zero.
C) The AC impedance of a capacitor is known as Reactance and as we are dealing with capacitor circuits, more commonly called Capacitive Reactance, X
C
. Graph shows variation of capacitive reactance with frequency.
D) V=V
0
sinωt
Q=CV
Where C is capacitance.
I=
dt
dQ
=C
dt
dV
=CV
0
ωcosωt
Thus there is a
2
π
phase difference between current and voltage.